1. Field of the Invention
The present invention relates to a technique for transmitting audio data through a packet network and, in particular, an audio gateway device.
2. Description of the Related Art
The IP (Internet Protocol) telephone services (IP Telephony) for transmission of audio data through a packet network has been popular. Besides, the movement of reducing a working cost of the existing telephone network of line switching type by unifying telephone services thereof with packet services by constructing a backbone of telephone network with a packet network has become active year after year.
In the telephone service using a packet network, a gateway device for transferring existing telephone audio data through the packet network is necessary. In such gateway device, an audio processing and a session control (session ON/OFF control) are performed. An example of the conventional audio gateway device is VoIPMedia Gateway Module, a production of AudioCodes corporation.
FIG. 6 is a block diagram showing a configuration of the conventional audio gateway device. As shown in FIG. 6, the audio gateway device includes PSTN (Public Switched Telephone Network) line terminating portion 41, audio data processing portion 42, packet network line terminating portion 43 and general purpose processor 45. In the conventional audio gateway device constructed as mentioned, UDP/IP (User Datagram Protocol/Internet Protocol) processing of all input packets is performed by processing the input packets by transferring them to general purpose processor 45 through processor bus 44 and performing the RTP (Real-Time Transport Protocol: RFC 1889. A standard for real-time transfer of various real-tie media of such as audio, video or other input data on an IP network) processing and the processing by a DSP (Digital Signal Processor) constituting audio data processing portion 42.
However, in a case where a gateway device capable of processing data of channels, for example, 700ch to 2000ch, is realized by using the above mentioned conventional audio gateway device in which all packets are temporarily processed by processor 45, a large amount of packets is processed by a software. Therefore, the processing performance of the gateway device is limited by the processing performance of the processor and the performance (data transfer speed, etc.) of processor bus 44. This is a practical problem.
Further, since the audio packet and the control packet are transmitted through same processor bus 44, there are other problems of delay of audio data and influence thereof on jitter.